Elastic wave generator



Feb. 16, 1965 s. R. RICH 3,169,508

ELASTIC WAVE GENERATOR Filed Jan. 16, 1963 2 Sheets-Sheet 1 FIG!INVENTOR STANLEY R. RICH ATTORNEY Feb. 16, 1965 s. R. RICH ELASTIC WAVEGENERATOR Filed Jan. 16, 1963 2 Sheets-Sheet 2 5| ST T SUPERHEA ER SO E26 INVENTOR.

STANLEY R. RICH BWZW ATTORNEY 3,169,508 ELASTIC wAva oannrznron StanleyRanch, west Hartford, Conn, assignonby 'm'esne assignments, to NorthernIndustries, *Iuc Dover, Del.,

a corporation-f Delaware Filed Jan. 16, 1963, Ser. No. 251,838 7 Claims.(Cl. 116-137) This invention relates in general to apparatus for generating high intensity elastic waves in a gaseous medium for industrialpurposes, and more particularly to the class of such apparatus whichdepends for its operation upon fluid dynamics in a structure havingparts fixed relative to one another, rather than upon relative motionbetween parts of a structure having relatively movable parts. i. J

Apparatus of the class to which the invention relates is generallycharacterized by jahollow acoustic resonator having an openingthereinto, and a gas nozzle confronting the opening for propelling astream of gastoward the opening to generate elastic wave energy Whilesuch apparatus is now available for continuous use over long periods oftime with dry'air or other gas, attempts to use a wet gas, such assaturated or wet steam, have not met with the same success becauseliquid collecting in the resonator interrupts the operation. The problemis not the same as is encountered'with steam Whistles which are intendedonly forintermittent operation, and can be mounted so that theirresonators have their open sides or ends at the bottom, and which,moreover, are designed for audible sound generating only; and areconsequently relatively large as compared with generators to which thepresent invention relates. The latter generators are preferably designedto operateiin the superaudible regions, or

in the upper audible regions (e.g., 8 lie/ sec. or'higher),

and consequently have resonators which a're'quite small as compared withaudible whistles. Furthermore, gasborne elastic wave generators forindustrial purposes should preferably be able to be mounted in anyconceivable position or orientation, and in many cases must be mountedwith their resonators open at the top. These considerations, takentogether with the requirement for the ability to be operatedcontinuously for longperiods of time, have heretoforesubstantiallyfprevented'the use of steam as the driving gasforthe'gas-driven fluid-dynamic class of generators of gas bor'neelastic wave energy for industrial purposes.

It is theprincipal object of the present invention to provide new andimproved apparatus of the fluid-dynamic class for generating elasticwaves in a gaseous medium, which can be operated continuously for longperiods of time with steam or other wet or liquid-bearing gas, as Wellas with any of the dry gases heretofore useful. Another object is toprovide such improved apparatus which can be made to operate in theultrasonic frequency range.

Additional objects are to provide such improved apparatus which isself-cleaning, which does not have severe dimensional tolerances, whichcan be operated in any position or attitude, which will be economical tobuild and operate, and rugged in construction, which will'requii'elittle or no maintenance, which will resist contamination duringoperation with foams, for example, which' will be easily cleaned,assembled and put into use, and which can be adapted to all types andkinds of gas-phase'applications of elastic wave power. v

According to thefinve'ntion in one of its more general aspects, there isprovided a new and improved apparatus for generating elastic waves in agaseous medium comprising a hollow acoustic resonator having an openingthereinto, means to propel a stream of gas at said opening forgenerating said waves, and means comprising a 3,169,508 Patented eh. '16, i965 of liquid at all times during operation of the apparatus.

According to 'the invention in one of its more particular aspects, thereis provided, in one embodiment, "an apparatus for generating elasticwaves in a gaseous medium comprising a hollow acoustic resonator havingan opening thereinto, means to propel 'a stream of gas at said openingfor generatingsaid'waves, means providing an 'annular'passa'ge thecross-sectional area of which progressively increases'substanti'ally-withthe radius thereof cou- "pled at its smaller end tosaid opening for exhausting the "gas ot'said stream and guiding saidwaves .to am ambient region, wave director means in register with thelarger end of said passage to direct'said exhaust gas and waves in acommon direction, and means comprising a separate passage from saidresonator to drain liquid from. said resonator substantially toward saidcommon direction.

Thisapparatus may conveniently be realized in a circular 'or cylindricalform which ispa'rticularly easyjto manufacture and assemble.

According to another aspect of the invention, the r'es- 'onator may berealized'in a separate part, which can be exchanged in a particularapparatus, so that a desired operating frequency can be chosen withoutchanging the entire apparatus, and this part can include the drain meansfor the particular resonator it'embo'dies.

According to still another aspect' of the'inventi'on, there 'isprovideda "system for generating elastic Waves 'in a gaseous mediumcomprising in combination, a hollow acoustic resonator havingan openingthereinto, a source of steamunder'pressure, riieans'connected to saidsource to propel a stream of steam at said opening for generating "said'Waves,"and means comprising'a separate passage from 'said resonator todrainliquid from said resonator.

The invention isparticularly useful for generating high intensityelasticwave energy in a gaseous medium, using either wet'ordry gas asthe source of driving energy. By the term high intensity is meantei'asti'c wave'energy inla gaseous medium '(e.g., sonic or ultrasonicenergy) atan intensity level upto' about db (.1 watt/cm?) or more. Bythe term gas it is meant to include-steam, air, nitrogen, carbondioxide, and the like, without limitation.

The invention will now be described with reference to the accompanyingdrawings, wherein: 1

FIG. 1 is an axial section through a generator according to theinvention;

'FIG. 2 is'an end view, on a reducedscale, of PEG. 1 as seen from theright-hand end of FIG. 1;

FIG. 3 is a cross-section on line 3-3 of FIG. 1; and

FIG. 4 is a system incorporating a generatorv according to FIGS. 1-3,inclusive.

Referring to FIGS. 1-3, inclusive, a first cylindrical body 10, having aconvex conical surface 11 and first axial bore lz passing through it,confronts a second cylindrical body 15 having a concave conicalsurface16 and Y a second axial bore llpassing through'it. These'two bodies aremounted one tothe other by stand-off posts 18, 19, which may be weldedor otherwise fastened in place, so that the convex and concave surfaces11 and A cylindrical elongated resonator part 20 is located in the bore12 of the first body 10. The resonator part has at one end a resonatorcavity 21,'of which one end 22 confronting the second body 15 is open;the other end 23 is closed except for a vent passage 24 of smallerdiameter than the resonator cavity which extends from the closed end 23through the remainder of the resonator part 20. The resonator part 20 isheld in the bore 12 by a set screw 25. A somewhat hemispherical cover 26is fitted over the right-hand ends of the first body and the resonatorpart 20, for streamlining purposes. This cover has a vent passage 27through'it in axial register with the vent passage 24 from the resonator21-, and is held in place by a second set screw 28.

The bore 17 in the second body is fitted with a gas nozzle 30confronting the open end 22 of the resonator cavity 21. This nozzlecomprises a hollow cylindrical part 31 which fits tightly into the bore17, and has its inner cross-section tapered to a smaller diameter as itapproaches the resonator cavity 21, and a solid cylindrical part 32axially disposed within the'hollow part to provide an annular gaspassage 33 confronting the resonator cavity. The outer diameter of thegas passage is approximately the same as, or slightly smaller than, the

diameter of the open end 22 of the resonator cavity. The

nozzle parts 31 and 32 are held together by a spanner bar 34 which isfitted into two diametrically-opposite slots 36, 37 in the end of thehollow member 31 remote from the resonatorcavity 21, and in a slot 38 atthe corresponding end of the solid part 32. The region at the end 3970fthe bore 17 most remote from the first body 10 may be internallythreaded, for attachment to a feed pipe 41 for gas or steam (as shown inFIG. 4).

A wave director 42, having a cylindrical collar part 43 and an integralbell part 44 holds the second body 15 in the collar part. The base 45 ofthe collar part is apertured for passage of a gas feed pipe (not shownin FIG. 1). The bell part 44 has its inner surface at the collar part 43in register with the concave surface 16 of the second body 15, fromwhich the bell part flares outward from the axis AA and projects forwardto envelop the first body 10 and its contents.

The generator apparatus of the present invention may be operated in asystem as illustrated in FIG.. 4. A source of steam 50 may be connectedby a pipe 51 to a superheater 52 and thence via another pipe 41 to thegenerator. With -a generator according to the present invention thesuperheater 52 is optional, since the generator can be operated with wetsteam. Practical embodiments of the generator shown in FIGS. 1-3,inclusive, use /2 to pound of steam per minute at 30 to 40 p.s.i.(gauge). a

In operation, the driving gas from the nozzle passage 33 cooperates withthe resonator cavity 21 to produce gas-borne elastic wave energy in aknown manner. Ex haust gas and the generated elastic wave energy passthrough the annular passage defined by the conical walls 11 and 16 tothe bell part 44 of the wave director, which directs both forward overthe first body 10 and the cover 26.

Any liquid which enters the resonator cavity 21 can readily and withoutdelay escape via the liquid drain vent passages 24 and 27. The bottom 23of the resonator cavity is desirably tapered toward the vent passage 24,to facilitate the escape of liquid. The diameter of the vent passage 24is so small, relative to the wavelength of elastic wave energy in air atthe operating frequency, typically about 0.060 inch at frequencies up toabout 25 kc./sec., for example, that the elastic wave energy cani notpropagate through the vent passage, while liquid and gas can escapethrough it. The vent passage may be regarded as a vent which is so smallrelative to the bore of the resonator cavity 21 that it functions as anacoustic inductance of which the reaotance, jwM, is large com-KLw7=2Trf; I M=rnass of air (or other gas) in the vent column; and =theoperating frequency.

The length of the vent passage 24 does not'appear to be critical;however, it can readily be made to be t/4 relative to the wavelength ofthe elastic wave energy being generated, if desired.

It will be recognize that liquid will escape via the vent passage 24regardless of the orientation or attitude of the generator. If its axisAA is vertical, liquid will obviously pour out of the resonator cavity21. If the axis AA is horizontal, liquid will be blown out by gas fromthe nozzle 30. This will not interfere with or degrade the elastic-Wavegenerator function of the apparatus. Further, there is no need to matethe meeting surfaces of the resonator part 20 and the cover 26 (when thelatter is used); since liquid in the space between them has no effect onthe generation of elastic wave energy. Liquid in that space readilyescapes in any. event, due either to gravity or to gas escaping throughthe passages 24 and 27.

Apparatus according to the invention has been successfully usedrepeatedly on an industrial scale with steam, both wetand dry, air underpressure and contaminated with oil, and other liquid-bearing gases.

As is well-known, the frequency of operation is deter mined essentiallyby the depth of the resonator cavity 21. Typical depths for frequenciesin the range 8,000 to 24,000 cycles per second, in a cavity inch indiameter,

(a) for frequencies of the order of 20 kc./sec.: inch (b)for frequenciesof the order of 12 kc./sec.: inch These depths are measured to thebeginning of the taper in the bottom 23. As has been indicated above,the diameter of the vent passage 24 may typically be about 0.60 inch.

The apparatus may be made of any suitable material. Stainless steel ofthe 300 series is preferred.

The embodiments of the invention which have been illustrated anddescribed herein are but a few illustrations of the invention. Otherembodiments and modifications will occur to those skilled in the art. Noattempt has been made to illustrate all possible embodiments of theinvention, but rather only to illustrate its principles and the bestmanner presently known to practice it. Therefore, while certain specificembodiments have been described as illustrative of the invention, suchother forms as would occur to one skilled in this art on a reading of.the foregoing specification are also within the spirit and scope of theinvention, and it is intended that this invention includes allmodifications and equivalents which fall within the scope of theappended claims.

What is claimed is:

1. Inapparatus for generating elastic waves in a gaseous medium with anacoustic resonator cavity, an opening at one end of said cavity andmeans to pnopel a stream of gas at said opening for generating saidWaves, the improvement comprising, a comically shaped wall means in saidcavity opposite said opening, said wall means providing a vent column ofgenerally uniform cross-section smaller than the cross-section of saidcavity and extending away from the wall means in said cavity oppositesaid opening for draining liquid from said resonator, said cross-sectionof said vent column being so small that said vent column functions as anacoustic inductance, with respect to said waves, of which the reactancejwM is large compared with the acoustic impedance of said resonatorcavity, where uw 27rf; f the frequency of said waves; and M =mass of gasin said vent column.

from said opening, and means providing a vent column of generallyuniform cross-section extending away'frorn said other end of saidpassage for draining liquid from said resonator, said cross-section ofsaid vent column being so small that said vent column functions as anacoustic inductance, with respect to said waves, of Which't'ne reactancejwM is large compared with the acoustic impedance of said resonatorcavity, where f=the frequency of said waves; and yi=rnass of gas in saidvent column.

3. Apparatus according to claim 1 in w hich said cavity is cylindrical,said opening is at one end of the cylinder and said vent column is atthe other end of said cylinder and extends straight on the cylinder axisaway from said resonator. i

4. Apparatus according to claim 2 in which said cavity is cylindrical,said opening is at one end of the cylinder and said vent column is atthe other end of said cylinder and extends straight on the cylinder axisaway from said resonator. I V

5. Apparatus according to claim 3 in which said means to propel a streamof gas at said opening provides an annular stream of gas the outerdiameter of which is not larger than the diameter of said resonator.

6. Apparatus according to claim 1 in combination with a source of steamunder pressure connected to said means to propel a stream of gas at saidopening.

7. Apparatus according to claim 1 in which said source of steam includesa steam sunerneater.

References Cited by the Exaer UNi'iLi) s'rArEs PATENTS 84,239 11/63Wfiinmaiin 116-137 1,930,171 11/34 Amy Q 116-137 2,238,663 4/41Wellenstein 116l37 2,788,656 4/51 Sander 73-24 2,944,029 7/59 Jones eta1 116-137 3,664,619 1 1/62 Fortman Q 116- 137 3,081,979 3/63 Lindsey259-1 FOREIGN PATENTS 70,342 11/58 France. 1

' 749,021 11/44 Germany.

Louis I. CAPOZI, Primary Examiner.

1. IN APPARATUS FOR GENERATING ELASTIC WAVES IN A GASEOUS MEDIUM WITH ANACOUSTIC RESONATOR CAVITY, AN OPENING AT ONE END OF SAID CAVITY ANDMEANS TO PROPEL A STREAM OF GAS AT SAID OPENING FOR GENERATING SAIDWAVES, THE IMPROVEMENT COMPRISING, A CONICALLY SHAPED WALL MEANS IN SAIDCAVITY OPPOSITE SAID OPENING, SAID WALL MEANS PROVIDING A VENT COLUMN OFGENERALLY UNIFORM CROSS-SECTION SMALLER THAN THE CROSS-SECTION OF SAIDCAVITY AND EXTENDING AWAY FROM THE WALL MEANS IN SAID CAVITY OPPOSIRESAID OPENING FOR DRAINING LIQUID FROM SAID RESONATOR, SAID CROSS-SECTIONOF SAID VENT COLUMN BEING SO SMALL THAT SAID VENT COLUMN FUNCTIONS AS ANACOUSTIC INDUCTANCE, WITH RESPECT TO SAID WAVES, OF WHICH THE REACTANCEJWM IS LARGE COMPARED WITH THE ACOUSTIC IMPEDANCE OF SAID RESONATORCAVITY, WHERE "W"=2$F; "F"=THE FREQUENCY OF SAID WAVES; AND "M"=MASS OFGAS IN SAID VENT COLUMN.